[Babul]

since only 1 checkpoint can be shown at a time, the streamer decides which one is closest to a player, regardless of other checkpoints having a far higher stream distance, which you seem to use as "priority".
so i assume your mission checkpoints distances are set to a quite high value, the streamer "ignores" the far-away SF-checkpoint, therefore streaming one close-by in LV.
one solution could be: lower all mission checkpoints distance values to like 100.0 so the "new main target" can get assigned a temporary increased stream distance.
problem: as soon you pass another close checkpoint (<100 meters), it will make the SF one disappear until you leave the 100-radius again.

hm.. much effort, less reward. why dont you use a race checkpoint btw? it can use that "goal flag" plotted in the CP aswell, and it works together with regular checkpoint(s streamed).
only minor issues: the race-mission-target-CP will overlap with the already existing mission-cp, so you need to play with the distances for one of those checkpoints to make it disappear, or remove it (mission cp) while the target (race cp) is overlapping.
oh, and iam assuming that the player in that mission, isnt participating in a race aswell lol

edit: <3ThoseWallsOfText